Optical communication network and protection methods

ABSTRACT

Optical systems of the present invention are configured in optical networks including a plurality of optical switch nodes interconnected by a plurality of optical transmission fibers, or other waveguides. The transmission fibers in the network can provide working and/or protection capacity for information, or communications traffic, being transmitted through the network. In various embodiments of the network, multiple diverse, working routes are provided on a single fiber path interconnecting a plurality of switch nodes. The multiple, diverse working routes can then be protected using a common protection fiber or path to provide shared protection. The switch nodes include optical switch configured to provide various levels of optical switching depending upon the network configuration. For example, line switches as well as optical cross-connects and routers can be deployed in the present invention to switch one or more wavelengths between the working and protection fibers. The optical systems can be further configured to carry lower priority traffic on the protection fibers or wavelengths during normal operation to increase the overall normal operating capacity of the system.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation in part of commonly assignedU.S. Provisional Patent Application Serial No. 60/096,779 filed Aug. 17,1998, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] The present invention is directed generally to opticaltransmission networks. More particularly, the invention relates tooptical transmission systems including protection capability for use inoptical communication networks.

[0003] Communications transport systems are used to transportinformation over a substantial portion of the world. This extensivecommunication access requires enormous amounts of equipment to providethe necessary infrastructure for the systems. In addition, much of theequipment and almost all of the transport media is remotely located andnecessarily exposed to the environment.

[0004] In view of the necessary exposure of transmission systems touncontrolled environments, it is not uncommon for failures to occuralong a transmission path. However, if communication systems are to beeffective it is necessary to have a high degree of reliability in thesystem. Thus, communication systems must provide for protection of theinformation being transmitted through the systems, as well as forrestoration of failed links in the system.

[0005] The reliability of service provided by a transmission system isinversely proportional to the frequency of failures in the transmissionsystem. One of the most common failures in fiber optic transmissionnetworks is a fiber break. When a fiber break or other failure occurs ina transmission link, the traffic intended to pass through the link mustbe rerouted through another path until the link is restored. Anothercommon source of failures in optical transmission network is anequipment failure. The amount of traffic that is lost upon an equipmentfailure depends upon the particular piece of failed equipment in thenetwork. For example, in most, if not all, currently available fiberoptic transport networks, a line amplifier failure will result in acomplete loss of traffic traveling through an optical link containingthe failed line amplifier. Whereas, a transmitter or a receiver failurewill generally result only in the loss of the wavelengths associatedwith the failed transmitter or receiver.

[0006] Despite the persistent hazards of uncontrolled exposure toenvironmental conditions and inevitable equipment failures, it isimperative that communications service providers supply high qualityservice. Therefore, service providers have developed protection schemesto provide automatic traffic restoration upon a transmission linkfailure and have required redundant equipment systems to decrease theeffective failure rate of the link.

[0007] Protection schemes generally are categorized based on therelationship of a working channel and a protection channel and thetopology of the network. If information is transmitted through thenetwork on both a working channel and a protection channel, the schemesare referred to as providing one plus one (“1+1”) protection. Upon afailure of the working channel, the network switches to the protectionchannel. If information is switched from a working channel to protectionchannel or working path to a protection path when a failure occurs, theschemes are referred to as one for one (“1:1”) protection schemes. Moregenerally, M protection channels or paths can be shared between Nworking channels or paths, which is generally designated as M:Nprotection. Similarly, M protection channels can carry the sameinformation as the working channel to provide 1+M protection.

[0008] Protection schemes can be implemented using various multiplefiber switching topologies, which generally fall into two distinctclasses. The first class of protection schemes is referred to asUnidirectional Path-Switched Ring (“UPSR”) in SONET, or DedicatedProtection Ring (“DPRing”) in SDH. The second class is known asBi-directional Line-Switched Ring (“BLSR”) in SONET, or MultiplexSection-Shared Protection Ring (“MS-SPRing”) in SDH. UPSR and BLSRschemes can implemented using either electrical or optical switching,O-BLSR and O-UPSR.

[0009] In UPSR schemes, working fiber paths for each directionconnecting two nodes are on the same fiber ring and the protection pathsfor each direction are on a different fiber ring. Traffic from anorigination node is sent along both the working and protection paths toa destination node. In the event of a failure of the working fiber pathusing UPSR protection, the destination node electrically or opticallyswitches to the protection path to receive the traffic.

[0010] In BLSR schemes, transmission capacity of the ring fibers isdivided between working and protection capacities, which carry trafficin opposite directions. Communications traffic is sent betweenorigination and destination nodes using the working capacity of thering.

[0011] When a failure occurs, the nodes immediately adjacent to and onboth sides of the failure switch the traffic to the protection capacityon a different fiber, which propagates in the opposite direction.Traffic is looped back around the failure by the two proximate switchesusing the protection fiber generally without further reconfiguration ofthe system. In transoceanic BLSR applications, additional switching maybe performed to minimize the additional distance traveled by thererouted traffic.

[0012] BLSR is available in 2-fiber and 4-fiber implementations. In4-fiber implementations, a protection fiber is provided for each workingfiber and traffic is rerouted by switching between the working andprotection fibers. In the 2-fiber implementations, the working andprotection capacities are time division multiplexed (“TDM”) on the samewavelengths, when electrical BLSR switching is performed. When 2 fiber,optical BLSR switching is performed, wavelengths are allocated toworking channels on one fiber and to protection channel on the otherfiber to allow the wavelength to be multiplexed.

[0013] Also, some BLSR schemes allow lower priority traffic to betransported using the protection capacity to increase the systemcapacity and utilization efficiency during normal operation. Ifprotection switching is necessary, the lower priority traffic is droppedin favor of protecting the higher priority traffic.

[0014] As the demand for transmission capacity continues to grow, thereis an increasing need to efficiently use the available transmissioncapacity and protect the information being transported through thesystems. The increased amount. of traffic being carried on each fiberplaces increased importance on the ability to effectively protect theinformation, because each failure results in higher revenue losses forservice providers. Accordingly, there is a need for optical transmissionsystems and protection schemes that provide effective protection withincreasing wavelength efficiencies for use in long distancecommunication systems.

BRIEF SUMMARY OF THE INVENTION

[0015] The present invention addresses the need for higher reliabilityoptical transmission systems, apparatuses, and methods. Optical systemsof the present invention are configured in optical networks including aplurality of optical switch nodes interconnected by a plurality ofoptical transmission fibers, or other waveguides. The transmissionfibers provide working and/or protection capacity for information, orcommunications traffic, being transmitted through the network.

[0016] In various embodiments of the network, multiple diverse, workingroutes are provided on a single fiber path interconnecting a pluralityof the switch nodes. Shared protection for the multiple, diverse workingroutes can then be provided using a common protection fiber or path inthe system.

[0017] The switch nodes include optical switch configured to providevarious levels of optical switching depending upon the networkconfiguration. For example, line switches as well as wavelengthselective optical cross-connects and routers can be deployed as opticalswitches in the switch nodes. The optical switches are configured tointroduce, remove, and/or pass various signal wavelengths through theworking and protection paths. The switch nodes will function differentlydepending upon whether the node is an origination, destination, orintermediate switch node with respect to an individual signal wavelengthor group of wavelengths. The optical systems can be further configuredto carry lower priority traffic on the protection fibers or wavelengthsduring normal operation to increase the overall normal operatingcapacity of the system.

[0018] The use of optical switching at the switch nodes along theworking and protection paths connecting signal wavelength originationand destination nodes decreases the amount of redundancy necessary foroptical protection. Accordingly, the present invention addresses theaforementioned concerns by providing optical systems apparatuses, andmethods having increasingly flexible protection schemes. Theseadvantages and others will become apparent from the following detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Embodiments of the present invention will now be described, byway of example only, with reference to the accompanying drawings for thepurpose of illustrating embodiments only and not for purposes oflimiting the same; wherein like members bear like reference numeralsand:

[0020] FIGS. 1-3 show optical system embodiments.

DESCRIPTION OF THE INVENTION

[0021] Optical systems 10 of the present invention include a pluralityof optical switch nodes 12 that interconnect a plurality of opticaltransmission fibers, or other waveguides, 14 forming optical links 15between the optical nodes 12 (FIG. 1). As shown in FIG. 2, the opticallinks 15 can further include uni- and/or bi-directional opticalamplifiers 16 configured to optically amplify optical signals passingthrough the link 15 between the nodes 12 to overcome optical signalattenuation in the fiber 14.

[0022] As further shown in FIG. 2, the nodes 12 may include one or moretransmitters 18 and configured to transmit information via the opticalsignals (OS) carried by one or more information carrying signalwavelengths, or signal channels, λ_(i). The nodes 12 may further includeone or more optical receivers 20 configured to receive the opticalsignals OS from other nodes 12. The optical network 10 can be controlledvia a network management system 22, as well as by node to node controlschemes. In addition, the optical system 10 can be configured to provideuni-directional or bi-directional transmission in each fiber 14.

[0023] The transmitters 18 can transmit the information using directlyor externally modulated optical carrier sources or optical upconverters.The receivers 20 can include both direct and coherent detectionreceivers. For example, N transmitters 18 can be used to transmit Mdifferent signal wavelengths to J different receivers 20.

[0024] In various embodiments, one or more of the transmitters 18 andreceivers 20 can be wavelength tunable to provide wavelength allocationflexibility in the optical network 10. The transmitters 18 and receivers20 can be also connected to interfacial devices 24, such as electricaland optical cross-connect switches, IP routers, etc., to provideflexibility in transmitting and receiving information in the network 10.The interfacial devices 24 can be configured to receive, convert, andprovide information in one or more various protocols, encoding schemes,and bit rates to the transmitters 18, and perform the converse functionfor the receivers 20. The interfacial devices 24 also can be used toprovide edge protection switching in various nodes 12 depending upon theconfiguration. The optical system 10 may also include other opticalcomponents, such as one or more broadcast and/or wavelength reusableadd/drop devices disposed with the switch nodes 12 or separately alongthe transmission fiber 14.

[0025] Optical combiners 26 can be provided to combine optical signalsfrom different optical paths onto a common path. Likewise, opticaldistributors 28 can be provided to distribute optical signals from acommon path to a plurality of different optical paths. The opticalcombiners 26 and distributors 28 can include wavelength selective andnon-selective (“passive”) fiber and free space devices, as well aspolarization sensitive devices. Passive or WDM couplers/splitters,circulators, dichroic devices, prisms; gratings, etc. can be used alone,or in combination with various tunable or fixed, high, low, or band passor stop, transmissive or reflective filters, such as Bragg gratings,Fabry-Perot devices, dichroic filters, etc. in various configurations ofthe optical combiners 26 and distributors 28. Furthermore, the combiners26 and distributors 28 can include one or more serial or parallel stagesincorporating various devices to multiplex, demultiplex, and broadcastsignal wavelengths λ_(i) in the optical systems 10.

[0026] In optical systems 10 of the present invention, working capacityin the fibers 14 is allocated such that a common protection fiber pathcan be employed for a plurality of diverse working paths. In addition,at least a portion of the various paths can serve as working paths, aswell as protection paths by employing different wavelengths on eachfiber 14.

[0027] The optical switch nodes 12 are configured to provide eitherwavelength selective or line switching between the working andprotection fibers 14 entering and exiting the nodes 12. The switch nodes12 are operated differently depending upon whether the switch node 12 isan origination or destination node for the information, or the switchnode is intermediately disposed along the working or protection pathsbetween the origination and destination nodes. Origination switch nodesare configurable to switch optical signals being introduced into thenetwork 10 between working and protection paths, which provide diverseroutes to the destination switch node. Destination nodes areconfigurable to remove optical signals from the network 10 from eitherthe working and protection paths. Intermediate switch nodes areconfigurable to pass optical signals in the working and protectionwavelengths passing between the origination and destination nodes.

[0028] In various embodiments, optical line switches can be used tointerconnect the input fibers with the output fibers. Variousmechanical, acousto-optic, thermo-optic, and doped fiber switches, aswell as other line switches can be employed in the present invention.

[0029] Optical wavelength cross connect switches and routers can also beemployed to provide finer control over the signals being protectionswitched in the nodes 12. For example, U.S. Pat. No. 5,446,809 issued toFritz et al. discloses a wavelength selective switch that can be used inthe present invention. Other single wavelength cross-connect switchfabric that employ a non-selective switch fabric between wavelengthdemultiplexers and multiplexers can also be used as the optical switch.

[0030] In addition, commonly assign U.S. patent application Ser. No.09/119,562, which is incorporated herein by reference, discloses anoptical cross connect/router that provides for switching multiple signalwavelengths, or groups of wavelengths, from an input port to one or moreoutput ports. The wavelength selective switches/routers provideadditional flexibility in reconfiguring the network 10 in the event of afiber cut or other failure along one or more of the optical links 15.

[0031] An exemplary description of various protection schemes of thepresent invention is provided with reference to FIG. 1a&b, which showfour switching nodes 12A-D that may represent a portion of, or theentire, optical network 10. In normal operation, a first optical signal(OS1) at a first optical working wavelength λ₁ can enter the opticalnetwork 10 at optical switch node 12 _(A). The first optical signal OS1can be routed through a first fiber 14 ₁ and optical switch node 12 _(D)along a first optical path designated “A”, to optical switch 12 _(B),where it can exit the portion of the network 10 shown in the Figure. Inthis example, the first fiber 14 ₁ provides a working path for opticalsignals transmitted via switch node 12 _(A) to switch node 12 _(B)during normal operation.

[0032] Conversely, a second optical signal (OS2) at a second opticalworking wavelength λ₂ can enter the optical network 10 at optical switchnode 12 _(B). The second optical signal OS2 can be routed through asecond fiber 14 ₂ and optical switch node 12 _(D) along path A to node12 _(A), where can exit the network 10.

[0033] A third optical signal OS3 at the first optical workingwavelength λ₁ can be introduced into the optical network 10 onto thefirst fiber 14 ₁ at optical switch 12 _(B). The network 10 can beconfigured to remove the third optical signal OS3 at various pointsalong path B including switch node 12 _(A). As shown in FIG. 1a, thethird optical signal OS3 can be removed at switch node 12 _(C), therebyallowing a fourth optical signal (OS4) using the first wavelength λ₁ tobe introduced on the first transmission fiber 14 ₁. The fourth opticalsignal OS4 can be transmitted along path B to the optical node 12 _(A).Similarly, a fifth optical signal OS5 can be introduced along path B onthe second fiber 14 ₂ and transmitted to the optical node 12 _(B).

[0034] Because multiple signals are transmitted upon a single fiber pathconnecting at least three switch nodes, a single protection fiber can beshared by the multiple signals. In the event of a fiber cut, theorigination and destination switch nodes 12 of the optical signals inthe network 10 are reconfigured to route the optical signals through adifferent fiber along a different optical path between the originationand destination nodes. In FIG. 1a, optical signals OS1, OS3, and OS4being transmitted on the first fiber 14 ₁ can be protected by switchingthe respective signals to the second fiber 14 ₂. Likewise, opticalsignals OS2 and OS5 can be transmitted on the second fiber 14 ₂ can beprotected by switching the respective signals to the first fiber 14 ₁.

[0035] For example, if a fiber cut occurs at point X in FIG. 1b, opticalsignals being transmitted in path A have to be rerouted. Switch node 12_(A) is reconfigured to route the first optical signal OS1 through thesecond fiber 14 ₂ along path B. Switch node 12 _(B) is reconfigured toreceive the first optical signal OS1 from the second fiber 14 ₂.Furthermore, switch node 12 _(C) and any other switch nodes between theorigin and destination nodes, 12 _(A) and 12 _(B), are configured topass the first wavelength λ₁ on the second fiber 14 ₂ and the secondwavelength λ₂ on the first fiber 14 ₁. In this manner, optical signalsOS1 and OS2 are routed through path B along with optical signals OS3,OS4, and OS5 and bypass the fiber cut without having to loop back ontothe first fiber 14 ₁. The ability to optically reroute the opticalsignal from a working fiber to a protection fiber without having to loopback onto the first fiber provide increased flexibility in configurationof the optical system 10.

[0036] As shown in FIG. 3, the present invention can be implemented onmore expansive mesh architectures that provide a plurality of protectionpaths between switch nodes 12 _(A) and 12 _(B). For example, theembodiment shown in FIG. 3 provides three possible paths between switchnodes 12 _(A) and 12 _(B) that can be used to provide working andprotection capacity. Shared path protection can implemented between allof the switch nodes, thereby providing protection against multiple fibercuts disrupting service in the network. For example, the switch nodes 12can be configured to route the first optical signal through switch nodes12 _(D-F) in the event of service disruptions between switch node 12_(D) and 12 _(B), 12 _(C) and 12 _(B), and/or 12 _(A) and 12 _(C). Itwill be appreciated that the number of signal wavelengths λ_(i), as wellas the number of fibers 14 interconnecting the switch nodes will dependupon the capacity of the optical system 10.

[0037] Generally, the switch nodes 12 will be configured to merelyswitch the working wavelengths from the working fiber to the protectionfiber. Thus, the working wavelengths carrying the information will bethe same as the protection wavelengths in the system. However, theswitch nodes 12 can be configured to provide either optical orelectrical wavelength conversion or interchange, when a protectionswitch is performed. In those embodiments, the working wavelengths willnot necessarily be the same as the protection wavelengths in thesystems. It will be further appreciated that the switch nodes along theprotection path and at the destination node will have to be reconfiguredto handle the protection wavelength.

[0038] In the present protection scheme, the protection path orprotection path wavelengths can be used to carry lower priority trafficbetween various switch nodes 12 in the network 10. Upon a failure in oneof the link 15, the switch nodes are configured to drop the lowerpriority traffic and carry the protection traffic. In networks withmultiple protection paths, such as in FIG. 3 embodiments, lower prioritytraffic can be further partitioned among the possible protection pathswith the quality of service depending upon the probability of using aparticular protection path.

[0039] Those of ordinary skill in the art will appreciate that numerousmodifications and variations that can be made to specific aspects of thepresent invention without departing from the scope of the presentinvention. It is intended that the foregoing specification and thefollowing claims cover such modifications and variations.

What is claimed is:
 1. An optical system comprising: a first opticalnode configured to route a first optical signal at a first workingwavelength to a second optical node via a first optical path; a thirdoptical node configured to route a second optical signal at said firstworking wavelength to said first optical node via a second optical path;said first optical node being configurable to route the first opticalsignal at a first protection wavelength to said second optical node viaa third optical path providing optical communication between said firstoptical node and said third optical node coupled to a fourth opticalpath providing optical communication between said third optical node andsaid second optical node; and, said third optical node beingconfigurable to route the second optical signal at the first protectionwavelength to said first optical node via said fourth optical pathcoupled to a fifth optical path providing optical communication betweenthe second optical node and said first optical node.
 2. The network ofclaim 1, wherein the first working wavelength and the first protectionwavelength are the same wavelength.
 3. The network of claim 1, whereinsaid first optical node includes an optical switch configurable toprovide originating optical signals to one of said first and thirdoptical paths, remove optical signals destined for said first opticalnode from said second and fifth optical paths and pass optical signalsfrom said second and fifth optical paths to at least one of said firstand third optical paths.
 4. The network of claim 1, wherein said secondoptical node includes an optical switch configurable to provideoriginating optical signals to at least said fifth optical path, removeoptical signals destined for said second optical node from said firstand fourth optical paths and pass optical signals from at least saidfourth optical path to at least said fifth optical paths.
 5. The networkof claim 1, wherein said second node optically communicates with saidthird node via at least a sixth optical path.
 6. The network of claim 1,wherein said third optical node includes an optical switch configurableto provide originating optical signals to at least said second andfourth optical paths, remove optical signals destined for said thirdoptical node from at least said third optical path and pass opticalsignals from said third optical paths to at least said fourth opticalpath.
 7. The network of claim 1, wherein at least one of said first,second, and third optical nodes includes an optical switch configured toseparate and switch individual signal wavelengths from a plurality ofsignal wavelengths.
 8. The network of claim 1, wherein at least one ofsaid first, second, and third optical nodes includes an optical switchconfigured to separate and switch groups of signal wavelengthscomprising a subset of a plurality of signal wavelengths.
 9. The networkof claim 1, wherein each of said first, second, and third optical nodesincludes an optical switch configured to separate and switch at leastone signal wavelength from a plurality of signal wavelengths.
 10. Thenetwork of claim 1, wherein each of said first, second, third, fourth,and fifth optical paths includes at least one optical fiber configuredto carry optical signals.
 11. The network of claim 10, wherein at leastsaid first and second optical nodes are configured providebi-directional transmission of optical signals via said first opticalpath.
 12. An optical network comprising: a first optical node configuredto route a first optical signal at a first working wavelength to asecond optical node via a first optical path; a third optical nodeconfigured to route a second optical signal at said first workingwavelength to a fourth optical node via a second optical path; saidfirst optical node being configurable to route said first optical signalat a first protection wavelength to said second optical node via a thirdoptical path providing optical communication between said first opticalnode and said fourth optical node coupled to a fourth optical pathproviding optical communication between said fourth optical node andsaid third optical node and further coupled to a fifth optical pathproviding optical communication between said third optical node and saidsecond optical node; and, said third optical node being configurable toroute said second optical signal at said first protection wavelength tosaid fourth optical node via said fifth optical path coupled to a sixthoptical path providing optical communication between said second opticalnode and said first optical node, and further coupled to said thirdoptical path.
 13. The network of claim 12, wherein said first workingwavelength and said first protection wavelength are the same wavelength.14. The network of claim 12, further comprising a seventh optical pathproviding optical communication between said fourth optical node andsaid second optical node; and, an eighth optical path providing opticalcommunication between said first optical node and said third opticalnode.
 15. A method of protecting information transmitted in an opticalnetwork comprising: providing a plurality of switch nodes interconnectedby a plurality of optical transmission paths; configuring an originationswitch nodes to switch information being transmitted to a destinationswitch node between a working path and a protection path; switching thedestination node to receive the information from the appropriate one ofthe working path and the protection path; and, provisioning at least athird switch node to allow the information to pass between theorigination and destination nodes.